Optical disk having read-only and rewritable areas with overlapping formats

ABSTRACT

The optical disk of this invention includes a read-only area in which a plurality of read-only tracks are formed and a rewritable area in which a plurality of rewritable tracks are formed, wherein each of the plurality of read-only tracks is divided into a plurality of first sectors, a signal is prerecorded in at least one of the plurality of first sectors under a predetermined reproduction format, each of the plurality of rewritable tracks is divided into a plurality of second sectors, a signal is recordable in at least one of the plurality of second sectors under a predetermined recording format including the predetermined reproduction format, and the read-only area is located on an inner portion of the optical disk, while the rewritable area is located on an outer portion of the optical disk.

The present application is a continuation of U.S. patent applicationSer. No. 08/954,929, filed Oct. 21, 1997 and now U.S. Pat. No.6,078,559.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk, and more particularlyrelates to a rewritable optical disk having a control data signalrepresenting the type of the disk and the like recorded thereon.

2. Description of the Related Art

In recent years, various types of optical disks, for example, read-onlytypes such as a CD and a CD-ROM and types which allow for data recordingsuch as a data addition type and a rewritable type, have been widelyused. Some of such optical disks of the read-only type, the dataaddition type, and the rewritable type are the same in appearance andthe like, though they are different in type from each other.

Some of the optical disks are different from others in format type andparameters to be set at recording and/or reproduction. Information onthe format type and information for setting parameters is thereforeprerecorded as control data signals in a predetermined region of thedisk, so that the control data signals are read with a drive forreproducing/recording data from/on the optical disk before variousparameters are set for the drive.

A method for recording such control data signals on an optical disk willbe described, using a “130 mm rewritable optical disk” as an example.

The “130 mm rewritable optical disk” has a format defined by JIS X6271.Two types of formats are defined by the standard: i.e., Format A wherecontinuous grooves are formed spirally on a disk, and lands betweenadjacent grooves are used as tracks for recording signals; and Format Bwhere marks for sampling are formed on a disk to allow for trackingcontrol by a sample servo method. The two formats are common in theconfiguration of a control information track where the control datasignals are recorded. That is, the control information track isspecified to have a PEP region, an inner SFP region, and an outer SFPregion for the two formats.

The PEP region is located on the innermost portion of the disk, whereprerecord marks (also called embossed pits), obtained by modulating withlow-frequency phase-modulated recording codes, are used. All the marksin the PEP region are arranged so as to be aligned in the radialdirection of the disk. This arrangement is schematically shown in FIG.3A. Each prerecord mark and each space between adjacent prerecord marksare two channel bits long. One PEP bit cell has a length of 656±1channel bits. FIG. 4 shows forms of such PEP bit cells. The informationof the PEP bit cell is represented by a phase-modulated recording code.A PEP bit cell where marks are formed in the first half thereofrepresents logical 0, while that where marks are formed in the secondhalf thereof represents logical 1. A total of 561 to 567 PEP bit cellsof the above forms per track are recorded on the disk.

The PEP region has a track format shown in FIG. 5A, which includes threesectors. FIG. 5B shows a sector format of each sector. The numbers shownin FIGS. 5A and 5B represent the numbers of PEP bit cells allocated torespective signals. A data region of the sector format where variouscontrol signals are recorded has a capacity of 18 bytes (144 PEP bitcells) (hereinafter, bytes are referred to as “B”). For example, asignal representing the format (Format A or B) to be used by the disk isrecorded in byte 0. The details on other control signals to be recordedon the data region are specified in the aforementioned JIS standard. Thedescription thereof is therefore omitted here.

When the PEP region with the above format is illuminated with light withan optical head or the like, light is focused on a signal recordedsurface of the disk by focusing control. Since marks are aligned in theradial direction in the PEP area, signals can be reproduced withouttracking control.

FIG. 3A also shows an example of a beam track. The portion where nomarks are formed serves as a mirror, producing a large amount ofreflection light. The portion where marks are formed diffractsreflection light depending on whether or not the marks exist atrespective positions on the disk. Therefore, the average level of theamount of reflection light is low compared with that of the mirrorportion.

FIG. 3B shows a change in amount of reflection light. Since therepetition frequency of the marks is higher than the period of the PEPbit cells, mark signal components can be eliminated by limiting the bandfor a reproduction signal. The waveform of the reproduction signalobtained by band limit is shown in FIG. 3C. The information of each PEPbit cell can be detected by examining the level of the reproductionsignal.

Then, the inner and outer SFP regions of the control information trackwill be described. The same information is recorded in the inner andouter SFP regions. That is, prerecord marks are recorded in the innerand outer SFP regions under a standard user data format. A 512 B regionis allocated for the control data signals. For example, the sameinformation as the 18 B information recorded in the PEP regions isrecorded in bytes 0 to 17. The details on other control information tobe recorded in this region are specified in the aforementioned JISstandard. The description thereof is therefore omitted here.

FIG. 6 shows an example of the standard user data format of each sectorwhere the user data capacity is 512 B and Format A is used. The numbersshown in FIG. 6 represent the numbers of bytes (B) allocated torespective signals. The capacity of the data region becomes 650 Bincluding an error correction code, resynchronization bytes, and controlbytes in addition to the 512 B user bytes.

This sector for recording signals in the data region also includes thefollowing regions: a prerecorded address section composed of a sectormark (SM) indicating the head of the sector, a VFO region forsynchronizing clock reproduction, an ID region indicating the address ofthe sector, an address mark (AM) indicating the head of the ID region,and the like; and regions for rewriting data, such as an offsetdetection region (ODF), an ALPC used for detection of laser output, anda buffer region provided to avoid overlap with a subsequent sector.

The total capacity of the sector is therefore 746 B. Although thecontrol data recorded in the SFP regions are prerecord marks, thecapacity of 746 B is required to record the 512 B control signals, as inthe case of recording user data, since the control data is recordedunder the user data format.

In recent years, read-only optical disks in which digitized andcompressed image and sound signals are recorded have been proposed.FIGS. 7A to 7C show an example of a sector format of one of suchread-only optical disks called a DVD (digital video disk).

A 2048 B unit of information data such as image and sound is recorded inone sector. This unit is called a first data signal. The sector alsoincludes a 4 B data ID, a 2 B IED for error detection of the data ID, a6 B RSV as reservation, and a 4 B EDC for error detection of the entiresector. Such one sector including these regions is called a first dataunit. FIG. 7A shows a configuration of the first data unit which has adata length of 2048+4+2+6+4=2064 (B).

The information data (2048 B) is scrambled in the following manner. Ashift register is constructed so that so-called M-series data isgenerated. An initial value is set for the shift register, and issequentially shifted in synchronization with the data, so as to generatepseudorandom data. An exclusive-OR between the generated pseudorandomdata and the information data to be recorded is calculated every bit.Thus, the information data (2048 B) is scrambled.

A total of 16 sectors of the thus-scrambled first data units are puttogether to constitute an error correction code of Reed Solomon coding.In such an error correction code, each data unit constituting one sectoris arranged in an array of 172 B×12 rows and a total of 16 sectors ofsuch data units are put together to constitute an array of 172 B×192rows. A 16 B outer code is added to each column of the array, and then a10 B inner code is added to each row of the resultant array. As aresult, as shown in FIG. 7B, a data block of 182 B×208 rows (37856 B) isformed. This data block is called an ECC block.

The ECC block is then interleaved so that the 16 B outer codes areincluded in the respective sectors. Thus, the data capacity of eachsector becomes 182 B×13 rows =2366 B.

The resultant data is then modulated with a recording code. A RLL (runlength limited) code where the run length after modulation is limited isused as the recording code. As an example, a {fraction (8/16)}conversion code which converts 8-bit data into 16-channel-bit data isused. This conversion is conducted based on a predetermined conversiontable. According to this conversion, DC components included in therecording code can be suppressed by controlling the code selection,though the detailed description of this control is omitted here.

In this modulation, the minimum and maximum bit lengths are limited to 3and 11 channel bits, respectively. In order to secure synchronization atreproduction, a 2 B synchronization code is inserted every 91 B, i.e., ahalf of one row of 182 B. As the synchronization code, several differentcodes with a length of 32 channel bits having patterns which normally donot appear in the {fraction (8/16)} conversion code are predetermined.This period of 93 B data including the synchronization code is called aframe. This configuration is shown in FIG. 7C. Thus, the data capacityof each sector is now 186 B×13 rows=2418 B.

In a read-only DVD having a single signal recording surface, data isrecorded by forming pits on the disk from the inner circumferencethereof toward the outer circumference at a constant linear velocity(i.e., by CLV driving) in accordance with the above-described sectorformat. A read-only DVD having double signal recording surfaces has alsobeen proposed, though the description of data recording on such a diskis omitted here.

FIG. 8 shows a configuration of signal recording areas of the read-onlyDVD. A lead-in area is located on the innermost portion of the disk,which starts at a diameter of 22.6 mm. A data area where informationdata such as image and sound is recorded starts at a diameter of 24.0 mmand ends at a diameter of 58.0 mm at maximum. A lead-out area followsthe data area and ends at a diameter of 58.5 mm at maximum. The sectoraddress is 30000 in the hexadecimal notation (denoted as 30000h) at thehead of the data area, and increases by 1h every sector toward the outercircumference of the disk. In the lead-in area, the sector addressdecreases by 1h every sector toward the inner circumference of the disk.

The control information is recorded in the lead-in area under the sectorformat described above. In the lead-in area, a reference code which isused for identification of the disk manufacturer, reproductionadjustment, and the like is recorded over two ECC blocks covering sectoraddresses starting from 2F0000h to 2F020h. The control data is recordedover 192 blocks covering sector addresses from 2F200h to 2FE00h. In theother sectors in the lead-in area, information data is recorded as 00hunder the sector format described above.

A rewritable DVD which is compatible in format with the above-describedread-only DVD has been proposed. In such a rewritable optical disk,spiral or concentric grooves are formed on a disk substrate, and arecording film is formed on the substrate to define tracks along thegrooves. In order to maximize the recording capacity, both grooves andlands between adjacent grooves are used as recording tracks.

Each track is divided into a plurality of sectors as units for datarecording and reproduction. Address information is added to each sectorso that the position of required information data can be managed tofacilitate high-speed data retrieval. More specifically, a header regionwhich includes an ID signal representing the address information of thesector is provided at the head of the sector.

In order to secure the compatibility with the read-only DVD, therewritable DVD has a format so that the 2418 B data of one sector of theread-only DVD can be recorded in a user data region of one sector of therewritable DVD as a unit. This 2418 B data is called a second datasignal.

The sector format for the rewritable DVD also requires an ID regionindicating the address number of the sector and a buffer region, as inthe case of the optical disk according to the aforementioned JISstandard. The total capacity of the sector including these regions ispreferably a multiple of the frame length (93 B) of the format for theread-only disk.

FIG. 9 shows an example of the format for the rewritable DVD whichsatisfies the above requirements. The 2048 B data (first data signal) isarranged under a format similar to that used f or the read-only DVDdescribed above, to obtain 2418 B data (second data signal), and theresultant 2418 B data is recorded in a data region 91 shown in FIG. 9. A1 byte postamble (PA) region 92 follows the data region 91. In the caseof the {fraction (8/16)} conversion code, the end of the recording codeshould be identified so that the converted data can be correctlydecoded. The PA is provided to identify the end of the recording code,and a pattern obtained by modulating a predetermined code in accordancewith a modulation rule is recorded.

A PS region 93 precedes the data region 91, where a presync signal isrecorded to indicate the start of the data region and obtain bytesynchronization. As the presync signal, a code with a length of 3 B (48channel bits) which has high autocorrelation is predetermined. A VFOregion 94 precedes the PS region 93, where a signal with a specificpattern is recorded to obtain prompt and stable clocking of a PLL(phase-locked loop) of a reproduction circuit.

The specific pattern of the signal is, for example, a repetition of a4-channel-bit pattern, i.e., “ . . . 1000 1000 . . . ” as represented inNRZI coding. The length of the VF0 region 94 is 35 B to secure thefrequency of the inversion and the duration required for stableclocking.

A first guard data region 95 precedes the VFO region 94, while a secondguard data region 96 follows the PA region 92. In a rewritable recordingmedium, the head and end portions of the recording area thereof degradeafter repeated recording and deletion. The guard data regions 95 and 96are therefore required to have a length large enough to prevent thedegradation from affecting the area from the VFO region 94 to the PAregion 92. It has been found from experiments that the lengths of thefirst and second guard data regions 95 and 96 should be 15 B and 45 B,respectively. Data to be recorded in these guard data regions are, forexample, the same repetition of the 4-channel-bit pattern as that usedfor the VFO region 94, i.e., “ . . . 1000 1000 . . . ”.

A gap region 97 is provided for setting a laser power. The length of thegap region 97 is 10 B to secure the time required for the setting of thelaser power. A buffer region 98 is provided to secure a time width whereno data is recorded to ensure that the end of the recording data doesnot overlap a subsequent sector even if a variation in rotation of adisk motor or disk eccentricity occurs. The length of the buffer region98 is 40 B.

The above regions 91 to 98 constitute an area where rewritable data isrecorded and has a total length of 2567 B. The signal recorded in thisarea is called a third data signal.

A 2 B mirror region 99 is provided to secure the time required fordetermining an offset of the servo tracking.

Next, a header region 100 will be described. As shown in FIG. 9, a firsthalf 19 and a second half 20 of the header region 100 are displaced fromthe center line of the groove in the opposite radial directions fromeach other by about a quarter of the pitch of the groove, so that theheader region can be read from both the groove track and the land track.The header region 100 includes total four sector ID signals (PIDs). Forthe groove track, for example, sector ID signals PID1 and PID2 in thefirst half 19 are displaced toward the outer circumference of the disk,while sector ID signals PID3 and PID4 in the second half 20 aredisplaced toward the inner circumference of the disk.

A 4 B Pid region representing the address information of the sector isprovided in each sector ID signal PID. In the Pid region, 3 B isallocated for the sector number and the remaining 1 byte is allocatedfor various types of information such as the PID number. In a Pid3region 113 and a Pid4 region 118, the address information of the sectoron the groove track having the center line from which the PIDs aredisplaced is recorded. In a Pid1 region 103 and a Pid2 region 108, theaddress information of the sector on the land track adjacent to thegroove track on the inner side thereof is recorded. IED regions 104,109, 114, and 119 with a length of 2 B represent an error detection codefor the preceding respective Pid regions. The data in the Pid regionsand the IED regions are modulated with the {fraction (8/16)} conversioncode described above. In order to identify the end of the conversioncode, 1 byte postamble (PA) regions 105, 110, 115, and 120 are provided.

AM regions 102, 107, 112, and 117 precede the respective Pid regions,where address mark signals are recorded to indicate the start of the Pidregions and obtain byte synchronization. Each address mark signal has alength of 3 B (48 channel bits), and a code having a pattern which doesnot appear in the {fraction (8/16)} conversion code is predetermined.

First and second VFO regions 101, 111, 106, and 116 are provided at theheads of the respective PIDs. As in the VFO region 94, the repetition ofthe 4-channel-bit pattern, “ . . . 1000 1000 . . . ” is used for theseVFO regions. In the header region 100, the first half including thesector ID signals PID1 and PID2 and the second half including the sectorID signals PID3 and PID4 are displaced in the opposite radial directionsas described above. Accordingly, in order to resume the bitsynchronization, the first VFO regions 101 and 111 located at the headsof the first and second halves of the header region 100 are made long.On the contrary, the second VFO regions 106 and 116 of the first andsecond halves may be short since they are only required forre-synchronization. For example, the lengths of the first and second VFOregions are 36 B and 8 B, respectively.

As a result, the total length of one sector of the rewritable DVD is2697 B. Thus, the length of one sector of the rewritable DVD is largerthan that of one sector of the read-only DVD by 279 B (corresponding tothree frames).

As described above, in the rewritable DVD, as in the read-only DVD, itis necessary to prerecord the control data signals indicating varioustypes of control information. This can be performed using the prerecordmarks, as in the case of the above-described “130 mm rewritable opticaldisk”, under the sector format used for the “130 mm rewritable opticaldisk”. The length of one sector of the rewritable DVD is larger thanthat of one sector of the read-only DVD by about 10% or more asdescribed above. Since the control data signals are recorded at thefabrication of the disk and will not be rewritten, this increase in thesector length is unnecessary for the recording of the control datasignals. This unnecessary increase in sector length is thereforedisadvantageous for DVDs which are demanded to have a large capacity.

A drive for DVD disks is required to be able to record and/or reproduceboth read-only DVDs and rewritable DVDs However, the read-only DVDs andthe rewritable DVDs are different in sector format. The type of the diskmounted in the drive can be identified by reading the control datasignal. However, in order to read the control data signal, the format ofthe disk must be identified to locate the recorded position of thecontrol data signal.

In order to identify the type of the disk, a region with the same sectorformat may be set for both the read-only type and the rewritable typeusing rerecord marks so as to record a signal indicating the type of thedisk in the region, as in the case of the PEP region of theabove-described “130 mm rewritable optical disk”. This common region isfirst reproduced at the activation of the disk to identify the type ofthe disk. Once the type of disk is identified, the control data on thedisk can be reproduced in accordance with the format for the disk.However, as in the case of the “130 mm rewritable optical disk”, thesignal indicating the type of the disk recorded on the common area isthe signal recorded as part of the control data signal. Recording thesame control data signal on two different regions results in redundancyof the recording area. The redundancy of the recording area isdisadvantageous for DVDs which are demanded to have a large capacity.

In view of the foregoing, the objective of the present invention is toprovide an optical disk in which control data signals are recorded undera format which can be easily read regardless of the type of the-opticaldisk, a read-only DVD or a rewritable DVD, and redundancy is reduced toimprove the recording capacity.

SUMMARY OF THE INVENTION

The optical disk of this invention includes a read-only area where aplurality of read-only tracks are formed and a rewritable area where aplurality of rewritable tracks are formed, wherein each of the pluralityof read-only tracks is divided into a plurality of first sectors, asignal is prerecorded in at least one of the plurality of first sectorsunder a predetermined reproduction format, each of the plurality ofrewritable tracks is divided into a plurality of second sectors, asignal is recordable in at least one of the plurality of second sectorsunder a predetermined recording format including the predeterminedreproduction format, and the read-only area is located on an innerportion of the optical disk, while the rewritable area is located on anouter portion of the optical disk.

In one embodiment of the invention, the plurality of first sectors ofthe plurality of read-only tracks are aligned in a radial direction ofthe optical disk.

In another embodiment of the invention, a pit array is formed in theread-only area, spiral or concentric grooves are formed in therewritable area, and the depth of the pit array is substantially thesame as the depth of the grooves.

In still another embodiment of the invention, a reference signal forreproduction adjustment is prerecorded in the first sectors of thenumber equal to a multiple of the number of first sectors included inone error correction block, and the first sectors where the referencesignal is prerecorded are located within one cycle of the read-onlytrack.

In still another embodiment of the invention, the rewritable areaincludes a data area where user data is recordable, a lead-in areahaving a zone for test recording, and a lead-out area having a zone fortest recording, and the lead-in area is located on an inner side of thedata area, and the lead-out area is located on an outer side of the dataarea.

Alternatively, the optical disk of this invention includes a read-onlyarea where a plurality of read-only tracks are formed and a rewritablearea where a plurality of rewritable tracks are formed, wherein each ofthe plurality of read-only tracks is divided into a plurality of firstsectors, a signal is prerecorded in at least one of the plurality offirst sectors under a predetermined reproduction format, each of theplurality of rewritable tracks is divided into a plurality of secondsectors, a signal is recordable in at least one of the plurality ofsecond sectors under a predetermined recording format including thepredetermined reproduction format, the read-only area is located on aninner portion of the optical disk, while the rewritable area is locatedon an outer portion of the optical disk, and a connection zone isprovided between the read-only area and the rewritable area, neither thesignal under the predetermined reproduction format nor the signal underthe predetermined recording format is recorded in the connection zone.

In one embodiment of the invention, the width of the connection zone inthe radial direction is set smaller than an amount of eccentricity ofthe optical disk.

In another embodiment of the invention, an address increased by oneaddress from an address of a last sector in the read-only area is usedas an address of a head sector in the rewritable area.

Alternatively, the optical disk of this invention is compatible with aread-only optical disk which includes a read-only area having aplurality of read-only tracks, each of the plurality of read-only tracksbeing divided into a plurality of first sectors, signals beingprerecorded in at least one of the plurality of first sectors under apredetermined reproduction format. The optical disk includes a read-onlyarea where a plurality of read-only tracks are formed and a rewritablearea where a plurality of rewritable tracks are formed, wherein each ofthe plurality of read-only tracks is divided into a plurality of firstsectors, a signal is prerecorded in at least one of the plurality offirst sectors under a predetermined reproduction format, each of theplurality of rewritable tracks is divided into a plurality of secondsectors, a signal is recordable in at least one of the plurality ofsecond sectors under a predetermined recording format including thepredetermined reproduction format, and the read-only area is located onan inner portion of the optical disk, while the rewritable area islocated on an outer portion of the optical disk.

In another embodiment of the invention, an address of a sector forrecording a control data signal is the same as an address of a sectorfor recording a control data signal of the read-only optical disk.

In still another embodiment of the invention, an address of a headsector in the rewritable area is the same as an address of a head sectorin a data area of the read-only optical disk.

In still another embodiment of the invention, a radial position of ahead sector in the rewritable area is the same as an radial position ofa head sector in a data area of the read-only optical disk.

In still another embodiment of the invention, a logical address of asector in a data area of the rewritable area is obtained by adding alogical address to a physical address of a head sector in the data area.

In still another embodiment of the invention, a logical address of ahead sector in a data area of the rewritable area is the same as anaddress of a head sector in a data area of the read-only optical disk.

Thus, according to one aspect of the present invention, the optical diskincludes the read-only area where a plurality of read-only tracks areformed and the rewritable area where a plurality of rewritable tracksare formed. Each of the plurality of read-only tracks is divided into aplurality of first sectors. A signal is prerecorded in at least one ofthe plurality of first sectors under a predetermined reproductionformat. Each of the plurality of rewritable tracks is divided into aplurality of second sectors. A signal is recordable in at least one ofthe plurality of second sectors under a predetermined recording formatincluding the predetermined reproduction format. The read-only area islocated on the inner portion of the optical disk, while the rewritablearea is located on the outer portion of the optical disk.

Accordingly, the control data signal is recorded in the read-only areawhere a region for recording header information is not provided. Thismeans that the control data signal is recorded under the reproductionformat for the first sectors in the read-only area which is lower inredundancy than the sector format for the second sectors in therewritable area. This improves the efficiency of the recording region ofthe rewritable optical disk.

Also, the optical disk according to the present invention is compatiblewith the read-only optical disk, and includes the read-only area where aplurality of read-only tracks are formed and the rewritable area where aplurality of rewritable tracks are formed. Each of the plurality ofread-only tracks is divided into a plurality of first sectors. A signalis prerecorded in at least one of the plurality of first sectors under apredetermined reproduction format. Each of the plurality of rewritabletracks is divided into a plurality of second sectors. A signal isrecordable in at least one of the plurality of second sectors under apredetermined recording format including the predetermined reproductionformat. The read-only area is located on the inner portion of theoptical disk, while the rewritable area is located on the outer portionof the optical disk.

Accordingly, the control data signal is recorded in the read-only arealocated on the inner portion of the optical disk, as in the case of theread-only optical disk, under the same sector format as that used forthe read-only optical disk.

As a result, a drive which is compatible with both the rewritableoptical disk and the read-only optical disk can reproduce data fromwhichever optical disk mounted in the drive, the rewritable optical diskor the read-only optical disk, under the same format. The drive can alsodetect the control signals recorded on both the rewritable optical diskand the read-only optical disk, and activate these optical disks easily.This eliminates the necessity of providing a special region such as thePEP region described above.

Thus, the invention described herein makes possible the advantage ofproviding an optical disk where control data signals are recorded undera format which can be easily read regardless of the type of the opticaldisk is, a read-only DVD or a rewritable DVD, and redundancy is reducedto improve the recording capacity.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a layout of areas of an optical diskaccording to the present invention.

FIG. 2 is a schematic view of an appearance of the optical diskaccording to the present invention.

FIG. 3A schematically shows an array of marks in a PEP region of aconventional optical disk,

FIG. 3B shows a change in reflection light amount, and

FIG. 3C shows a waveform of a reproduction signal obtained after bandlimit.

FIG. 4 is a schematic view of forms of bit cells in the PEP region ofthe conventional optical disk.

FIGS. 5A and 5B are schematic views of a track format and a sectorformat, respectively, of the PEP region of the conventional opticaldisk.

FIG. 6 is a schematic view of a sector format of a conventional opticaldisk.

FIGS. 7A, 7B, and 7C are schematic views of sector formats of aread-only area of the optical disk according to the present invention.

FIG. 8 is a schematic view of a layout of areas of a conventionalread-only DVD.

FIG. 9 is a schematic view of a sector format of a rewritable area ofthe optical disk according to the present invention.

FIG. 10 is a schematic view showing the boundary portion between therewritable area and the read-only area of the optical disk according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described by way of examplewith reference to the accompanying drawings.

While the present specification uses DVDs as an example, it should beunderstood to be applicable to CDs and other media.

As an example of the optical disk according to the present invention, arewritable DVD which is compatible in format with the conventionalread-only DVD described above will be described. The appearance of theoptical disk is shown in FIG. 2. Referring to FIG. 2, an optical disk 1has a center hole 2 and a rewritable area 3 for recording data. Spiralgrooves are formed on the rewritable area 3, and the grooves and landsbetween adjacent grooves are used as tracks. A read-only area 4 isprovided on the inner side of the rewritable area 3. In this example, acontrol data zone 5 where control data representing various types ofdetailed information on the disk is provided in the read-only area 4.

The sector format shown in FIGS. 7A to 7C described above is used forthe read-only area 4. That is, a 2048 B first data signal together witha data ID, an error correction code, a synchronization code, and thelike constitute data with a sector length of 2418 B. The resultant datais prerecorded on the disk as a pit array.

The sector format shown in FIG. 9 described above is used for therewritable area 3. That is, user data is divided into 2048 B units offirst data signals. Each first data signal is transformed into a 2418 Bsecond data signal having the same configuration as the format for theread-only area shown in FIG. 7C. Data required to provide therewritability is added to the second data signal to obtain a 2567 Bthird data signal. A space for recording this size of data is secured ona track, and a 128 B header region and a 2 B mirror region are added tothe third data signal, thereby to obtain a rewritable sector with atotal length of 2697 B. According to this format shown in FIG. 9,therefore, the 2418 B data of one sector of the read-only DVD can berecorded in the user data region of one sector of the rewritable DVD asa unit without any change.

In order to indicate the address numbers of the two sectors on theadjacent groove and land tracks, the first half 19 and the second half20 of the header region of the rewritable area are displaced from thecenter line of the groove in the opposite radial directions from eachother by about a quarter of the pitch of the groove.

In order to achieve the above arrangement, the header regions on thetracks need to be aligned in the radial direction of the disk. Thisarrangement results in having the same number of sectors for all tracksincluding inner and outer tracks, thereby reducing the recording densityof the outer tracks.

In order to overcome the above problem, the rewritable area is dividedinto a plurality of zones. The number of sectors per track is the samewithin each zone, and is increased by one sector as the zones are closerto the outer circumference of the disk.

For example, when data is recorded on a phase-change recording materialunder the format shown in FIG. 9 using a semiconductor laser with awavelength of 650 nm and an objective lens with an NA of 0.6, theminimum bit length of about 0.41 μm is realized. If the radial positionof the innermost end of the rewritable area is set at 24.0 mm which issubstantially the same as the radial position of the innermost end ofthe data area of the read-only disk, 17 sectors can be formed on eachtrack in the innermost zone. By increasing the number of sectors pertrack by one sector for each zone while the minimum bit length is keptsubstantially the same, a total of 24 zones are obtained for a disk witha diameter of 12 cm, and 40 sectors are formed on each track in theoutermost zone. In this case, the total user data capacity of the diskis about 2.6 GB.

When data is recorded on/reproduced from the disk with the above sectorarrangement, the following two driving methods may be employed: an MCAVdriving method in which, while the disk is rotated at a constantrotational speed, the frequency of the recording/reproduction is changedevery zone; and a ZCLV driving method in which the rotational speed ischanged every zone so that the linear velocity is substantially the sameamong the zones, while it is fixed within each zone.

Hereinbelow, a mastering process for fabricating the disk with the aboveformat will be described. The mastering includes recording signalsaccording to the format using a light source with a short wavelengthsuch as a gas laser while rotating a glass plate applied with aphotosensitive agent (resist).

An EO modulator or the like is irradiated with laser light from thelight source. When electric signals according to the format is appliedto the EO modulator, the intensity of the light passing through the EOmodulator is modulated. The modulated light is focused with theobjective lens onto the glass plate to illuminate the photosensitiveagent.

By developing the glass plate, prerecord pits and grooves are formed onthe glass plate. A metal mask is formed by plating using the plate as aresist original disk. A resin disk substrate is then formed based on themetal mask, though detailed description is omitted here. In thismastering process, a turn table for rotating the glass plate rotateswith high precision. Accordingly, a turn table with a large inertiaforce is used, and thus it is difficult to change the rotational speedinstantaneously during the mastering.

In this example, as described above, the read-only area 4 is provided onthe inner portion of the disk as shown in FIG. 2. The same sector formatas that used for the read-only DVD is used for the read-only area 4.

However, the read-only DVD is driven by the CLV driving method where thelinear velocity is constant as described above, while the rewritable DVDis driven by the MCAV or ZCLV driving method. If the different drivingmethods are employed for the read-only area and the rewritable area,switching of the rotational speed is required. Switching of therotational speed during the mastering of the disk is difficult asdescribed above.

In this example, therefore, data is recorded on the read-only area at aconstant rotational speed of the disk. The read-only area of theresultant disk is driven by the same driving method as that for therewritable area, i.e., the MCAV or ZCLV driving method. Since thesectors in the read-only area are arranged at the constant rotationalspeed, the period of the reproduction of the sectors becomes constant.As a result, even if the address of a sector fails to be reproduced, itcan be easily interporated from the positions of the preceding andfollowing sectors.

The thickness of the photosensitive agent applied to the glass plate inthe mastering process is made substantially uniform. This thicknesscorresponds to the depth of the grooves in the rewritable area.

For example, the depth of the grooves in the rewritable area isdetermined to be optically about λ/8 so as to obtain a large trackingsignal. In the read-only area, the depth of the grooves, whichcorresponds to the depth of the pits, is determined to be opticallyabout λ/4 so as to obtain a large contrast of reproduction signals. Thedepth of the pits in the read-only area is therefore larger than that ofthe grooves in the rewritable area. It is difficult to change the depthof the grooves and the pits between the read-only area and therewritable area of the same disk. In this example, therefore, the depthof the pits in the read-only area is made substantially the same as thedepth of the grooves in the rewritable area.

More specifically, the depth of the pits in the read-only area is madesmaller than the depth of the pits in the read-only disk (opticallyabout λ/4). To compensate for the failure in obtaining a large contrastof the reproduction signals, the length of the shortest pits is madelarger than that of the read-only disk. For example, the length of theshortest pits is 0.41 μm which is the same bit length as that used inthe rewritable area.

In this example, the sector format is different between the rewritablearea and the read-only area. For example, while the length of the sectoris 2418 B in the read-only area, it is 2697 B in the rewritable area.The innermost zone of the rewritable area has 17 sectors per track. Thenumber of sectors per track in the read-only area when the minimum bitlength is substantially the same is calculated as follows.

17×2697/2418=18.9 . . .

In consideration of the facts that the read-only area is located nearerthe inner circumference of the disk than the rewritable area and thatthe number of sectors per track should be an integer, the number ofsectors per track in the read-only area is determined to be 18 sectors.

In this example, the track pitch is substantially the same in therewritable area and the read-only area. FIG. 10 schematically shows thetracks at the boundary between the rewritable area and the read-onlyarea. Portion (a) denotes the read-only area and portion (b) denotes therewritable area. In the read-only area (a), prerecorded pits 11 areformed along each track 10. A track pitch Tp 12 is determined by thedegree of crosstalk of the reproduction signals and the like. Forexample, the track pitch is 0.74 μm in the read-only DVD.

In the rewritable area (b), grooves 14 are formed. The grooves are usedas groove tracks 17 and lands between the grooves are used as landtracks 18. A track pitch Tp 13, which is a gap between the adjacentgroove track and land track, is substantially the same as the trackpitch 12 in the read-only area.

The groove pitch is therefore double the track pitch. The track widthsof the groove tracks and the land tracks are made substantially thesame. Therefore, the groove width and the track pitch should besubstantially the same. In order to form wide grooves, the laser beamused in the mastering process for recording data needs to be large inthe radial direction.

When such a wide beam is used in the read-only area, the resultant pitsare large in width, thereby narrowing the gap between the adjacent pits.This increases crosstalk of the reproduction signals. To avoid thisproblem, two different laser beams are used, where one of the laserbeams is small for recording small pits in the read-only area and theother is large for forming grooves in the rewritable area.

However, at the switching of the laser beams for pits and for grooves atthe boundary between the rewritable area and the read-only area, if thespot positions of the two laser beams on the disk surface are deviatedfrom each other, the recorded pit array and the groove are not formed insuccession, but overlap each other or are spaced apart from each other.It is practically difficult to put the spot positions of the two laserbeams in conformity with each other two-dimensionally on the disksurface. It is therefore impossible to connect the rewritable area andthe read-only area with the same track pitch at the boundary thereof.

In the read-only area, the pit array is continuously recorded startingfrom the innermost end of the area. At the outermost end of theread-only area, therefore, errors may be accumulated, and thus theposition of the end of the last sector may be shifted.

In this example, therefore, a connection zone is provided between therewritable area and the read-only area as shown as portion (c) in FIG.10. This connection zone of a first example constitutes a flat (mirror)zone since no signal is recorded. Positioning of the two beams ispractically possible when the width of the connection zone is 1 μormore.

If the connection zone is wide, a tracking error signal is not generatedwhen the connection zone is irradiated with laser light for servotracking at the reproduction of data from the resultant disk with adrive. This makes the operation unstable. More specifically, when a diskis mounted on a drive and rotated, eccentricity more or less occurs. Ifthe size (width in the radial direction) of the mirror zone is smallerthan the minimum amount of the eccentricity, the laser beam from thedrive necessarily crosses the pit array in the read-only area or thegroove in the rewritable area during one rotation of the disk. Theallowance of the eccentricity amount for a normal disk is about ±50 μmat maximum. Therefore, in consideration of the minimum amount of theeccentricity, the width of the mirror zone in the radial direction maybe about 5 μm. The mirror zone with this width corresponds to 2 to 8tracks when calculated with the above track pitch. In FIG. 10, virtualtracks 15 are shown in the connection zone (c).

A second example of the connection zone according to the presentinvention will be described. The first example of the connection zoneconstitutes a mirror zone as described above. In the second example ofthe connection zone, dummy data is recorded. As the dummy data, therepetition of the 4-channel-bit pattern, “ . . . 1000 1000 . . . ”, usedfor the VFO region shown in FIG. 9 is used.

The dummy data is recorded along the tracks 15 shown in FIG. 10 coveringtwo to three tracks. Then, one or two empty grooves without headerregions are recorded (two to four tracks), followed by the formation ofsectors with header regions. With this configuration, even if the spotpositions of the laser beam are deviated from each other by about 1 μm,only the dummy data and the empty grooves overlap each other, notdestroying necessary data. By forming such a pit array, a tracking errorcan be detected stably in the connection zone.

In a third example of the connection zone according to the presentinvention, the dummy data in the connection zone has a sectorconfiguration. For example, when dummy data under the format for theread-only area is recorded, sectors as shown in FIG. 7 where the, firstuser data is all 00h are formed. When dummy data under the format forthe rewritable area is recorded, grooves of sectors with the headerregions as shown in FIG. 9 are formed. With this configuration, as inthe above two examples, even if the spot positions of the laser beam aredeviated from each other by about 1 μm, only the sectors of dummy dataoverlap each other, not destroying necessary data. By forming the pitarray as dummy data, the tracking error can be detected stably in theconnection zone.

Even if part of a sector fails to be read, no problem arises since it isdummy data. It is possible to set so that the addresses of the sectorsin the connection zone are not usable. By forming such a sector array inthe connection zone, a tracking error can be stably detected. Moreover,since the sector addresses can be detected, the positions of therespective sectors on the disk are identified, thereby facilitating thesystem management.

FIG. 1 shows a layout of the areas of the rewritable optical diskaccording to the present invention. In FIG. 1, respective zones in theareas are listed in the order from the inner side to the outer side ofthe disk, together with the rough radial position of each zone, theaddress of the head sector of each zone, the number of blocks includedin each zone, the number of tracks in each area, and the data ID numberindicating the logical address of data in head sector of each zone. Thesector address indicates the physical address of the sector, which isrecorded in the Pid regions of the header region for each sector in therewritable area and recorded as the data ID number for each sector inthe read-only area.

The data ID number indicates the logical address of the data recorded inthe sector. In the lead-in area and the lead-out area, the physicaladdress and the logical address of each sector are the same. In each ofthe rewritable sectors in the lead-in and lead-out areas, the data IDnumber included in the rewritable data region (second data signalregion) is the same as the physical address of the sector. The sectorsin the data area are all rewritable sectors. The data ID number in eachof these sectors indicates the logical address of data recorded in thesector.

Referring to FIG. 1, the read-only area is located on the inner portionof the disk. The innermost end of the read-only area is at a diameter of22.6 mm of the disk, as in the case of the read-only DVD. The rewritablearea starts at a diameter of 24.00 mm of the disk, as in the case of thedata area of the read-only DVD, and expands to the outer circumferenceof the disk.

The sector address is 30000 in the hexadecimal notation (denoted as30000h) at the head of the rewritable area, and increases by 1h everysector toward the outer circumference of the disk. In the read-onlyarea, the sector address decreases by 1h every sector toward the innercircumference of the disk. A portion of the rewritable area over 256 ECCblocks (4096 sectors) from the head thereof is used for testing of thedisk and the drive and the like. This portion of the rewritable area isincluded in the lead-in area which starts from the innermost end of theread-only area.

The data area follows the lead-in area for effecting therecording/reproduction of user data. The data area is divided into 24zones from zone 0 to zone 23. The address of the head sector in the dataarea is 31000h. The lead-out area follows the data area.

Hereinbelow, the respective areas will be described in detail.

In the read-only area portion of the lead-in area, a reference signalzone for recording a reference code is provided over one ECC blockcovering sector addresses starting from 2F000h to 2F010h. The referencecode is used for identification of the disk manufacturer, reproductionadjustment, and the like. A control data zone for recording control datasignals is provided over 192 blocks covering sector addresses startingfrom 2F200h to 2FE00h. The other portions of the read-only areaconstitute blank zones, where the first data signal is recorded as 00hin each sector under the same sector format as that used for the otherportions.

In this way, the same sector addresses as those used for the read-onlyDVD described above are used for the control data zone of the read-onlyarea of the rewritable optical disk according to the present invention.With this arrangement, it is possible for a drive compatible with thesetwo types of disks to always seek the same sector addresses to reproducethe control data signals from the sectors of the same addresses.Therefore, such a drive compatible with the two different types of diskscan follow the same procedure to activate these disks.

The connection zone follows the read-only area to obtain a smooth shiftfrom the read-only area to the rewritable area. As described above, inthe first example of the connection zone, the mirror zone is providedover a portion corresponding to two to eight tracks. Since no signal isrecorded in the mirror zone, the last sector of the final blank zone ofthe read-only area is the sector immediately before the sector address30000h of the head sector in the rewritable area. The address of thelast sector of the final blank zone is therefore 2FFFFh. The final blankzone includes 32 blocks covering sector addresses from 2FE00h followingthe control data zone to 2FFFFh.

In the second example of the connection zone, the connection zoneincludes dummy data and empty grooves having no sector address asdescribed above. Accordingly, the address arrangement as that in thefirst example of the connection zone can be used.

In the third example of the connection zone, the dummy data has a sectorconfiguration. The addresses of the sectors in the connection zone maybe preset to be unusable. The connection zone preferably has an integernumber of tracks and corresponds to an integer number of blocks.

For example, when the connection zone has eight tracks, it correspondsto nine blocks. In this case, the number of blocks in the final blankzone preceding the connection zone is reduced by nine blocks to 23blocks (sector addresses from 2FE00h to 2FF6Fh). The nine blocks isadded to the connection zone, to add a region covering sector addressesfrom 2FF70h to 2FFFFh to the connection zone. As a result, theconnection zone is a zone covering sector addresses from 2FF70h to30000h.

Although no address was allocated to the first and second examples ofthe connection zones, it is possible to allocate addresses to theconnection zones which have no sector configuration, as in the case ofthe third example of the connection zone.

The portion of the rewritable area located in the lead-in area followsthe connection zone. A guard track zone is first provided. The guardtrack zone starts at sector address 30000h and covers 32 blocks untilsector address 301FFh. The guard track zone prevents other data frombeing destroyed due to an error such as the tracking being off when atest signal is recorded in a subsequent disk test zone. No data isrecorded in the sectors in this zone.

The disk test zone is provided over the next 64 blocks covering sectoraddresses from 30200h to 305FFh for the testing of the disk quality andthe like by the disk manufacturer. A drive test zone is provided overthe next 112 blocks covering sector addresses from 30600h to 30CFFh forthe testing such as setting of a laser power in a drive. Another guardtrack zone is provided over the next 32 blocks covering sector addressesfrom 30D00h to 30EFFh for effecting functions similar to those of theabove guard track zone. A disk ID zone is provided over the next eightblocks covering sector addresses from 30F00h to 30F7Fh for recordingcopying management information. DMA 1&2 zones are provided over the nexteight blocks covering sector addresses from 30F80h to 30FFFh for diskdefect management.

The data area starts from the next address 31000h. The data area isdivided into 24 zones from zone 0 to zone 23 as described above. Eachzone is composed of 1888 tracks with an exception that zone 0 includesonly 1647 tracks because the portion covering 256 blocks (4096 sectors)from the head of the rewritable area belongs to the lead-in area asdescribed above. The number of blocks included in each zone is shown inFIG. 1 as an example. About 95% of the blocks in each zone are used asdata blocks for recording user data. The logical address of each sectorincluded in the data blocks represents an address obtained by adding thelogical address to the physical address of the head sector in the dataarea (address 31000h in this example).

To the head and end of each zone in the data area, 48 to 80 sectors(corresponding to two or more tracks) are allocated as buffer sectors.Such buffer sectors are provided because at each boundary of zones theheader region sometimes fails to be continuous with the precedingsector, and therefore no data is recorded in the buffer sectors. Most ofthe remaining 5% of the blocks in each zone serve as spare sectors,which replace sectors in the data blocks when they become defective, tobe used as sectors for data recording.

The physical address of the sector is used for data recording changes bythe above replacement. However, the logical address (data ID number) ofthe user data does not change as described above. Accordingly, a tableassociating the physical address of the sector with the logical addressis prepared and recorded in the DMA zones.

The lead-out area follows zone 23, starting from the sector address16B480h and expanding to the outermost circumference of the disk.Substantially the same zones as those in the portion of the rewritablearea located in the lead-in area are allocated for the lead-out area.DMA 3&4 zones are first provided at the head of the lead-out area fordisk defect management as described above. Thus, the four DMA zones, theDMA 1&2 zones on the inner side and the DMA 3&4 zones on the outer side,sandwich the data area. A disk ID zone is provided over the next eightblocks covering sector addresses from 16B500h to 16B57Fh for recordingcopying management information.

A guard track zone is provided over the next 32 blocks covering sectoraddresses from 16B580h to 16B77Fh. No data is recorded in this zone. Adrive test zone is provided over the next 112 blocks covering sectoraddresses from 16B780h to 16BE7Fh for the testing such as setting of alaser power in a drive. A disk test zone is provided over the next 112blocks covering sector addresses from 16BE80h to 16C57Fh for the testingof the disk quality and the like by the disk manufacturer. Another guardtrack zone is provided for over 3343 blocks covering sector addressesfrom 16C580h to 17966Fh. No data is recorded in this zone.

Thus, as is observed from the layout of the areas of the optical diskaccording to the present invention, the rewritable area starts at adiameter of 24.00 mm of the disk as in the case of the data area of theread-only DVD. The address of the head sector in the rewritable area isthe same as the address of the head sector in the data area of theread-only DVD. Also, the addresses of the sectors in the control datazone is the same as the addresses of the sectors in the control datazone of the read-only DVD. With this arrangement, it is possible for adrive compatible with these two types of disks to always seek the samesector addresses to reproduce the control data signals from the sectorsof the same addresses. Therefore, such a drive compatible with the twodifferent types of disks can follow the same procedure to activate thesedisks. As a result, effective control of the drive is realized.

An alternative example of the layout of the rewritable area of therewritable optical disk according to the present invention will bedescribed. The logical address of each sector included in the datablocks of the data area is the same as the address of each sector in thedata area of the read-only DVD. While the address of the head sector inthe data area of the read-only DVD is 30000h, the physical address ofthe head sector in the data area of the rewritable optical diskaccording to the present invention is 31000h.

In this alternative example, the logical address of the head sector inthe data area is set at 30000h so as to be the same as the address ofthe head sector in the data area of the read-only DVD. The logicaladdress of each sector in the subsequent data blocks is obtained byadding the logical address to the logical address of the head sector(30000h in this alternative example).

With this address setting, the logical addresses of the sectors in thedata blocks overlap the addresses of the sectors in the portion of therewritable area located in the lead-in area. This problem can be solvedby adding to the data ID number of each sector the type of the area thesector belongs to, so that whether the sector is in the lead-in area orin the data area can be judged.

Thus, in the alternative example according to the present invention, thelogical addresses of the sectors the data blocks in the data area arethe same as the addresses of the sectors in the data area of theread-only DVD. With this arrangement, it is possible for a drivecompatible with these two types of disks to always seek the same sectoraddresses to reproduce the control data signals from the sectors of thesame addresses. Therefore, such a drive compatible with the twodifferent types of disks can follow the same procedure for theactivation of these disks. As a result, effective control of the driveis realized.

In the above examples according to the present invention, the formatshown in FIGS. 7A to 7C was used as the sector format for the read-onlyarea, and the format shown in FIG. 9 was used as the sector format forthe rewritable area. The sector formats are not restricted to these, butthe sector format for the “130 mm rewritable optical disk” describedabove can also be used.

Thus, the optical disk according to the present invention includes theread-only area where a plurality of read-only tracks are formed and therewritable area where a plurality of rewritable tracks are formed. Eachof the plurality of read-only tracks is divided into a plurality offirst sectors. A signal is prerecorded in at least one of the pluralityof first sectors under a predetermined reproduction format. Each of theplurality of rewritable tracks is divided into a plurality of secondsectors. A signal is recordable in at least one of the plurality ofsecond sectors under a predetermined recording format including thepredetermined reproduction format. The read-only area is located on theinner portion of the optical disk, while the rewritable area is locatedon the outer portion of the optical disk.

Accordingly, the control data signal is recorded in the read-only areawhere a region for recording header information is not provided. Thismeans that the control data signal is recorded under the reproductionformat for the first sectors in the read-only area which is lower inredundancy than the sector format for the second sectors in therewritable area. This improves the efficiency of the recording region ofthe rewritable optical disk.

Also, the optical disk according to the present invention is compatiblewith the read-only optical disk, and includes the read-only area where aplurality of read-only tracks are formed and the rewritable area where aplurality of rewritable tracks are formed. Each of the plurality ofread-only tracks is divided into a plurality of first sectors. A signalis prerecorded in at least one of the plurality of first sectors under apredetermined reproduction format. Each of the plurality of rewritabletracks is divided into a plurality of second sectors. A signal isrecordable in at least one of the plurality of second sectors under apredetermined recording format including the predetermined reproductionformat. The read-only area is located on the inner portion of theoptical disk, while the rewritable area is located on the outer portionof the optical disk.

Accordingly, the control data signal is recorded in the read-only arealocated on the inner portion of the optical disk, as in the case of theread-only optical disk, under the same sector format as that used forthe read-only optical disk.

As a result, a drive which is compatible with both the rewritableoptical disk and the read-only optical disk can reproduce data fromwhichever optical disk mounted in the drive, the rewritable optical diskor the read-only optical disk, under the same format. The drive can alsodetect the control signals recorded on both the rewritable optical diskand the read-only optical disk, and activate these optical disks easily.This eliminates the necessity of providing a special region such as thePEP region described above.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. An optical disk comprising a read-only area inwhich a plurality of read-only tracks are formed and a rewritable areain which a plurality of rewritable tracks are formed, wherein each ofthe plurality of read-only tracks is divided into a plurality of firstsectors, a signal is prerecorded in at least one of the plurality offirst sectors under a predetermined reproduction format, each of theplurality of rewritable tracks is divided into a plurality of secondsectors, a signal is recordable in at least one of the plurality ofsecond sectors under a predetermined recording format which includes thepredetermined reproduction format as a part thereof and further includesanother part specific to the predetermined recording format, and theread-only area is located on an inner portion of the optical disk, whilethe rewritable area is located on an outer portion of the optical disk.2. An optical disk according to claim 1, wherein the plurality of firstsectors of the plurality of read-only tracks are aligned in a radialdirection of the optical disk.
 3. An optical disk according to claim 1,wherein a pit array is formed in the read-only area, spiral orconcentric grooves are formed in the rewritable area; and the depth ofthe pit array is substantially the same as the depth of the grooves. 4.An optical disk according to claim 1, wherein the number of theplurality of first sectors is 18 per track.
 5. An optical disk accordingto claim 1, wherein an address of a sector for recording a control datasignal in the read only area is the same as an address of a sector forrecording a control data signal of a read-only optical disk.
 6. Anoptical disk according to claim 1, wherein an address of a head sectorin the rewritable area is the same as an address of a head sector in adata area of a read-only optical disk.
 7. An optical disk according toclaim 1, wherein a radial position of a head sector in the rewritablearea is the same as a radial position of a head sector in a data area ofa read-only optical disk.
 8. An optical disk according to claim 1,wherein a reference signal for reproduction adjustment is prerecorded inthe first sectors of the number equal to a multiple of the number offirst sectors included in one error correction block, and the firstsectors where the reference signal is prerecorded are located within onecycle of the read-only track.
 9. An optical disk according to claim 3,wherein the plurality of first sectors are aligned in a radial directionof the optical disk.
 10. An optical disk according to claim 3, whereinthe number of the plurality of first sectors is 18 per track.
 11. Anoptical disk according to claim 3, wherein an address of a sector forrecording a control data signal in the read only area is the same as anaddress of a sector for recording a control data signal of a read-onlyoptical disk.
 12. An optical disk according to claim 3, wherein anaddress of a head sector in the rewritable area is the same as anaddress of a head sector in a data area of a read-only optical disk. 13.An optical disk according to claim 3, wherein a radial position of ahead sector in the rewritable area is the same as a radial position of ahead sector in a data area of a read-only optical disk.
 14. An opticaldisk according to claim 3, wherein a reference signal for reproductionadjustment is prerecorded in the first sectors of the number equal to amultiple of the number of first sectors included in one error correctionblock, and the first sectors where the reference signal is prerecordedare located within one cycle of the read-only track.